In my opinion, your best option is non-stop on Continental from EWR, as Barcelona has only three non-stop flights from the United States: CO from EWR, Delta from JFK, and, seasonally, US Airways from PHL. With a one-stop, options go up considerably.

If you want a bargain way to get the Barcelona and not too concern about the level of service or comfort...

Try FlyGobeSpan.com which will be flying daily between JFK-LPL and from there book a seat with a low cost carrier...

Ryanair can fly you from Liverpool - Barcelona/Gerona for about £20 each way or if you want to fly to Barcelona's main airport easyJet fly to BCN from LPL for about £35 each way. As both airlines have hubs at Liverpool.

Flights with FlyGlobeSpan are about £120 each way including taxes even during the summer!

If you want business class accross the Atlantic try SilverJet between EWR and LTN for about £799 return (inc tax) and book flights from LTN on to Barcelona with Ryanair or Easyjet as both again have hubs at LTN.

Depends on when you want to travel. It is more expensive in summer. In May, you can get from BOS-BCN for less than $700 RT on IB, AA, and LH. If you would rather travel from JFK, AF, AA, and BA offer flights for less than $700 RT and DL's nonstop is $900. Also for less than $700 if you don't mind flying a combination of CO and TP. CO nonstop is less than $800.